Sea Urchin Identification Question

[archaeofish]

While diving at Salt Creek last weekend I saw a sea urchin at about 30 feet that was definitely not a red, purple or green urchin. Of course I didn't have my camera (headslap!) but I spent some time examining it and this was what I saw: it was light colored (tannish) and it was definitely alive (tube feet were moving), however it did not have any visible spines on it's dorsal surface. There were a number of shells and small pebbles stuck to it's dorsal surface, but the shape seemed a little rounder/more irregular than a green urching shell. I didn't pick it up, but I could see a number of very small spines around the edges of it's ventral surface. My best guess is that it was a heart urchin, but the descriptions that I've read usually place these much deeper. I can't find an image of the heart urchin's ventral surface, so I thought I would throw this description out and see if any of the invertebrate experts on the list had any suggestions?

[Greg Jensen]

Color and description sound like a heart urchin, and they have been found that shallow before.

[archaeofish]

Thank you Greg! That was only my third dive at Salt Creek and I was able to add two new species to my life list! (heart urchin and northern abalone in the wild!) Needless to say I was pretty excited at the end of the dive.